1. Field of the Invention
The present invention relates to an elastic wave device with a structure that suppresses transverse modes by using a piston mode and to a ladder filter including the elastic wave device.
2. Description of the Related Art
Elastic wave devices that use a piston mode to suppress transverse modes have been proposed. WO 2011/088904A1 describes a device in which each of electrode fingers of an interdigital transducer (IDT) electrode has a large-width region at an end thereof. Thus, low-acoustic-velocity regions are disposed on both sides of a central region in a direction in which the electrode fingers extend. High-acoustic-velocity regions are disposed outside of the low-acoustic-velocity regions. WO 2011/088904A1 also describes a method of forming a low-acoustic-velocity region by using a structure in which end portions of electrode fingers are stacked on a dielectric layer.
However, with exiting elastic wave devices using a piston mode, such as the device described in WO 2011/088904A1, it is difficult to sufficiently suppress all transverse modes.